We will study the molecules and cells involved in induction of B cell immune responses. To this end the properties of two different types of helper T cells will be studied, one type which helps B Cell responses via some antigen-specific mechanism, and another type, which helps B cell responses by secreting a non-specific stimulatory molecule(s). Properties to be studied will include the kinetics of action of the two types of help on B cell responses. We will also study the properties of soluble mediators isolated from these two types of cells. The mediators will be examined for their physico-chemical characteristics, and also for the presence on them of various antigenic determinants, such as immunoglobulin or Ia markers. Antisera will be raised against the mediators and used in vitro to find out which T cell reactions involve which factors. Molecules on the surface of B cells will also be studied, to find out which are important in stimulation of these cells. Antisera directed at immunoglobulin or Ia determinants, will be used to inhibit various B cell reactions. The properties of a T cell derived molecule which suppresses B cell responses will be examined, and compared with those of the two helper factors described above.